Interpretive Summary: Insect predators, which feed on pest insects and are produced and used to control such pests in greenhouse and field, may feed on a wide range of prey species. The nutritional value of different prey species to the predator may vary considerably, but there are no consistent means to assess this value. To determine the nutritional effects of different prey species on reproducing adult female spined soldier bugs over a period of three weeks, scientists with USDA, ARS, Center for Medical, Agricultural and Veterinary Entomology studied the content of bugs with regard to weights, total protein, total lipid (fat), and total yolk protein (representing egg contents). Weights and protein contents did not vary as bugs were fed different prey for different periods of time, but lipid contents did, increasing as reproduction decreased. Yolk protein contents varied over time when bugs were fed only one of the species of prey. The results indicate that lipid content may be a good indicator of the nutritional value of prey species to reproducing adult female bugs. This information may be used by scientists and insect producers to select the best prey to feed predator bugs to achieve rapid reproduction and large numbers in colonies. It may also be used by scientists and growers to determine whether the bugs will thrive in fields that predominantly contain any given species of prey insect.

Technical Abstract:
Preferences of female predators for various species of prey may not correlate with nutritional value of the prey, notably with regard to resulting rates of reproduction in the female predator. This study assessed the biochemical status of adult female Podisus maculiventris (Say) as affected by prey species. Colony-reared females were fed one of five species of natural or factitious prey: beet armyworm (Spodoptera exigua (Hübner)), fall armyworm (Spodoptera frugiperda (JE Smith)), cabbage looper (Trichoplusia ni (Hübner)), wax moth (Galleria mellonella (L.)), or yellow mealworm (Tenebrio molitor (L.)). Fresh weights and contents of lipid, protein, and yolk protein were compared over periods of 7, 15, and 22 d. Fresh weights and protein showed no significant differences by trial length or by prey species. Total lipid content was the most significant parameter in relation to time and species of prey, ranging from 5.3% to 15.5% of mean fresh weight. Female P. maculiventris varied significantly in total lipid content by prey species at 15 d and 22 d, and by week only when fed fall armyworm. Highest lipid contents were observed in females fed yellow mealworm, and lowest lipid contents in females fed cabbage looper and beet armyworm. Yolk protein content did not correlate with cumulative oviposition, but did vary with time in those females fed on the beet armyworm or the wax moth. Lipid content in female predators may vary inversely with reproductive potential or egg load, and offers a quantitative measure of food quality.